Distributed propulsion for guns

ABSTRACT

Propellant charges for weapons, especially for the small caliber type, made of grains consisting of two layers, an outer slow burning composition and an inner or core composition for the control of interior ballistics. The charges consist of a plurality of increments of such type grains which differ in the thickness and composition of the outer layer and the thickness and composition of the core resulting in better control of interior ballistics, such, for example, as the obtention of higher velocities at lower peak pressure.

United States Patent 1151 3,706,278

Stiefel et al. 1451 Dec. 19, 1972 [54] DISTRIBUTED PROPULSION FOR [56]References Cited GUNS UNITED STATES PATENTS [72] Inventors: LudwigStieiel, Philadelphia, Pa.;

Martin S. silverstein, Mest Mount, 2,072,671 3/1937 Foulke ..102/4O NJ.JamesF Kowalick southam 3,092,525 6/1963 Cook ..102/104 p 3,421,9311/1969 Reverandu... ..1(l2/l()4 2,289,318 7/1942 Pratt ..102/104 [73]Assigneez The United States of America as 2,575,871 11/1951 Gordon etal...l(l2/l()4 23: 3 by the Secretary of the Primary Examiner-Robert F.Stahl Att0rney-Harry M. Saragovitz et al.

[22] Filed:" Feb. 25, 1971 [21] Appl. No.: 118,739 [57] ABSTRACTPropellant charges for weapons, especially for the Related AppllcatlonData small caliber type, made of grains consisting of two [63]Continuation-impart of Ser. No. 818,140, April 21, l an outer PummgComposmon 1969 abandoned inner or core composition for the control ofinterior ballistics. The charges consist of a plurality of incre- [52]Us Cl 102/38 102/103 102/104 ments of such type grains which differ inthe thickness 149/3 and composition of the outer layer and the thickness[51] Int Cl F42) 5/16 and composition of the core resulting in bettercontrol [58] i 49/3 of interior ballistics, such, for example, as theobten 0 149/ 1 tion of higher velocities at lower peak pressure.

5 Claims, 1 Drawing Figure P AfTEIN TEH m 19 I972 \NVENTOR5 LUDW\6STiEF'EL. MART\N E5. $\L,\/ERSTE\N JAMES F. KOWALICK AT TURN EY5.

DlSTlRlBUTED PROPULSION FOR GUNS This application is acontinuation-in-part of our application Ser. No. 818,140, filed 21 Apr.1969, for Distributed Propulsion for Guns", now abandoned, and relatesto incremental propellant charges in the control of interior ballisticsfor small arms weapons wherein the propellant grains in a givenincrement will consist of two layers, a slower burning outer layer and afaster burning inner layer.

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto us of any royalty thereon.

At present, the gas generation rate of small arms propellants may bemodified through propellant composition, grain geometry, or deterrentcoatings, any of which are capable of changing the pressure-time curveproduced by the ammunition.

These current small arms ammunition charges are generally comprised ofone type and size of propellant grain. Our invention contemplatespropellant charges which comprise a plurality of increments, whereinpropellant grains of different sizes, shapes and com position may beused therein, i.e., the grains may be solid cylinders, perforatedcylinders, spheres, platelets or discs. Because of the very small sizesof the grains used in small arms ammunition, only grains of limitedgeometries heretofore could be economically manufactured. Consequently,the number of variables that could be manipulated to achieve a givenspecified performance was severely limited. Our invention, however, willpermit the manipulation of a large number of variables to obtain desiredcontrols. Furthermore, the charges can now be loaded in conventionalloading machinery, there being no barriers or separate packages orcapsules involved.

As aforediscussed, prior art small arms propellants are treated with adeterrent composition which is not a film or layer on the externalsurface of the grains, but a material which is absorbed into the outerportions of the grain matrix and thus serving to reduce the burning rateof outer portions of the grains.

In contrast therewith, our invention allows the gas generation scheduleto be controlled by permitting the programmed burning of the incrementswithout the use of any separately assembled barriers, capsules and thelike. With regard to these smaller caliber cartridges, such barriers orcapsules cannot readily be loaded into the narrow case necks, andfurthermore, the very short ballistic time results in incompletecombustion of the barriers or capsules, to thereby cause deposition ofunburned debris in the weapon, or the ejection of partially burnedmaterial from the gun. Our invention therefore, involves polymericfilms, or layers, or coatings applied to the outer surfaces of theindividual grains in such a way that the entire charge, including thescheduling coating is totally consumed by the time the bullet exits fromthe gun or weapon.

Briefly then, our invention lends versatility to propellant charges,especially small arms propellant charges, such that their gas generationschedule may be regulated by manipulating the thickness and burning rateof the outer layer and inner core respectively, as well as the numberand size of the increments.

It is therefore the principal object of this invention to provideimproved means for controlling the interior ballistics of weapons.

Other and further objects of the invention will be apparent to thoseskilled in the art upon study of this disclosure and wherein the singleFIGURE illustrates a sectional view of an embodiment of our small armscartridge.

Referring now to the drawing, a standard small arms cartridge 10includes a projectile l2, casing 14 and primer 16. While threeincrements only are shown, mixed uniformly, any reasonable number may beemployed. One of the increments comprises a ball propellant or innercore composition 20, although single and double base extrededpropellants may be used advantageously. The uncoated propellant isherein designated the inner core or faster burning composition. Anotherincrement 22 is comprised of grains having an inner core compositionwith an outer layer of a suitable resin or polymeric coating, which maysuitably comprise n-butyl methacrylate resin; methyl cellulose; orpolyvinyl acetate; and others.

These scheduling coating materials should be soluble or dispersable in asolvent that does not react adversely with the inner core compositionpropellant. Upon evaporation of the solvent, a polymerization orcrosslinking reaction should desirably occur to insolubilize thedeposited film or coating with respect to the solvent to preventsoftening of the previous layer when subsequent layers are applied. Thecoating solution will consist of about 5 to 15 percent solids by weightin the solvent, the exact concentration of coating solids in thesolution being dependent only on the requirements of the specificcoating process, for example, the types of spray devices being used. Theactual proportions of solvent to solids is of little concern and withinthe skill of the art since the solvent will have evaporated leaving thedeposited film, or layer, or coating on the desired surfaces.

Processes for coating our materials are many and varied. For example,the tablet coating process, fluidized bed process, airless sprayprocess, microencapsulation techniques, vacuum deposition, phaseseparation from aqueous as well as organic-solvent solutions,interfacial polymerization and melt techniques, and the like, may beemployed advantageously and successfully in carrying out our invention,while providing means for preventing the small grains from adhering toeach other while the film is drying.

A third increment 24 which may comprise the same materials as 22 is alsoincorporated into the charge. Regardless of the composition of the outermaterial, it will be slower burning than the outer layer used forincrement 22, by virtue of its composition or thickness. The propellantcontained within the coating may be identical with inner core 20 or thatused for increment 22, or may even be faster burning than either ofthese. Any air space remaining between projectile l2 and the propellantmay be packed with cotton 26.

The abovedescribed concept of charges consisting of increments ofdifferent types of overall propellant grains, where each coated grainconsists of an outer slower burning composition and a faster corecomposi tion to yield controlled interior ballistics by means of theburning rates and thicknesses of the outer composition and burning rateand thickness of the inner composition for each type used and byquantities of each type used in the complete charge is referred to asdistributed propulsion.

The products and processes of our invention are illustrated by thenon-limiting example hereinunder set forth, all percentages being byweight:

A 5.56mm cartridge, including a projectile weighing 56 grains, wasloaded with 27.8 grains of a standard double base rolled ball propellanthaving a cut of 0.027 inch/.016 inch (grain passed through a screenhaving 0.027 inch openings but was retained on a screen having 0.016inch openings) rolled to a uniform web of 0.015 inch, and a compositionas follows:

Composition:

Nitrocellulose (13.15% N) 81.59% Nitroglycerine 10.52 Dibutylphthalate5.68 Diphenylamine 0.98 Total Volatiles 1.23

The peak chamber pressure obtained was 49.0 kpsi (thousand pounds persquare inch) and the projectile velocity, measured at 15 feet from themuzzle, was 3100 fps. Measurement of the velocity at a distance of 15feet from the muzzle is accomplished by the standard 2-screen methodwhereby an average velocity at 15 feet from the muzzle is obtained usinga 10 foot base line.

EXAMPLE I 75/25 polyvinylbutyral/melamine formaldehyde resin Solvent:50/50 V/V l-leptaneethanol Coating Solution: 10% solids in the solution3rd Increment:

Weight: 5.6 grains Propellant: Identical with second increment Coating:

(a) Level:5% by weight of propellant (b) Data:

Solids: 75/25 polyvinylbutyral/melamine formaldehyde resin Solvent:50/50 V/V Heptaneethanol Coating Solution: solids in the solution Theseincrements were mixed and loaded into the 5.56mm cartridge case. The 25grains so mixed yielded a peak pressure of 48.9 kpsi and a velocity atfeet of 3160 fps. Although the peak pressures and velocities aresubstantially the same for our inventive distributed propulsioncartridge and the standard, our cartridge required only 25.0 grains toequal the performance of 27.8 rains f standar doubl b se ball ellant.Furthgr, the Tower loadi ng density 3f our ch ig of extruded propellantmakes it even more difficult to achieve the values of the standard.

We wish it to be understood that we do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

We claim: 1. In combination with a cartridge having a primer, projectileand case, the improvement therewith for providing good control ofinterior ballistics in a weapon system using said cartridge, saidimprovement comprismg a propellant charge disposed within said case andcomprising 7 4 a substantially uniform mixture of the propellant grainsof a plurality of increments of propellant grains, each grain of atleast one of said increments comprising two layers, said layerscomprising an outer slower burning composition and an inner fasterburning core composition, and each grain of at least one of saidincrements comprising at least one layer, said one layer being a corecomposition whose composition may be the same as or different from saidfirst mentioned core composition and which is faster burning than any ofsaid outer slower burning compositions, whereby upon ignition of saidpropellant charge, better control of interior ballistics is provided.

2. The cartridge of claim 1 wherein said cartridge is of 5.56mm size.

3. The cartridge of Claim 1 wherein said charge comprises a firstincrement of double base extruded propellant devoid of perforationstherethrough, a second increment of single base extruded propellantgrain, and a third increment of single base extruded propellant grainhaving a single perforation therethrough, said double base, extrudedpropellant comprising, by weight, 87.9 percent nitrocellulose having13.15 percent nitrogen, 9.8 percent nitroglycerine, 1.0 percentdiphenylamine, and 1.3 percent volatiles, and said single base extrudedpropellant grain comprising, by weight, 97.7 percent nitrocellulosehaving 13.15 percent nitrogen, 1.0 percent diphenylamine, and 1.3percent volatiles.

The cartridge of claim 3 wherein said first increment comprises 6.3grains, each of said grains having a 0.025 inch outside diameter and a0.025 inch length, said second increment has a single perforationtherethrough and comprises 13.1 grains, each of said second incrementgrains having an outer diameter of 0.030 inch, a length of 0.42 inch,and a perforation diameter of 0.007 inch with a 4 percent coating, byweight, therearound of /25 polyvinylbutyral/melamine formaldehyde, andsaid third increment comprises 5.6 grains, each of said third incrementgrains having dimensions equal to said second increment grains andhaving a 5 percent coating, by weight, therearound of 75/25polyvinylbutyral/melamine formaldehyde.

5. The cartridge of claim 4 wherein said cartridge yields a peakpressure of 48.9 kpsi and a projectile velocity at 15 feet of 3160 fps.

2. The cartridge of claim 1 wherein said cartridge is of 5.56mm size. 3.The cartridge of Claim 1 wherein said charge comprises a first incrementof double base extruded propellant devoid of perforations therethrough,a second increment of single base extruded propellant grain, and a thirdincrement of single base extruded propellant grain having a singleperforation therethrough, said double base, extruded propellantcomprising, by weight, 87.9 percent nitrocellulose having 13.15 percentnitrogen, 9.8 percent nitroglycerine, 1.0 percent diphenylamine, and 1.3percent volatiles, and said single base extruded propellant graincomprising, by weight, 97.7 percent nitrocellulose having 13.15 percentnitrogen, 1.0 percent diphenylamine, and 1.3 percent volatiles.
 4. Thecartridge of claim 3 wherein said first increment comprises 6.3 grains,each of said grains having a 0.025 inch outside diameter and a 0.025inch length, said second increment has a single perforation therethroughand comprises 13.1 grains, each of said second increment grains havingan outer diameter of 0.030 inch, a length of 0.42 inch, and aperforation diameter of 0.007 inch with a 4 percent coating, by weight,therearound of 75/25 polyvinylbutyral/melamine formaldehyde, and saidthird increment comprises 5.6 grains, each of said third incrementgrains having dimensions equal to said second increment grains andhaving a 5 percent coating, by weight, therearound of 75/25polyvinylbutyral/melamine formaldehyde.
 5. The cartridge of claim 4wherein said cartridge yields a peak pressure of 48.9 kpsi and aprojectile velocity at 15 feet of 3160 fps.